A detailed study is being made of the lipid and fatty acid composition and metabolism in reproductive tissue of male animals. The biosynthesis and interconversion of fatty acids is being studied in testes of animals, particularly the rat, in vivo and in vitro. Changes brought about in these metabolic processes by age, diet, pathological conditions, and hormonal influences are being determined. Studies will be extended to the epididymis. These studies seek to understand the relationship of cellular structure to these processes and the role of the polyenoic acids in the physiological function of male reproductive system. Studies of these types are being done not only on total testicular tissue but also in specific cell types separated by elutriation centrifugation or by filtration on nylon screen following enzymatic treatment.